Another way to extract useful information from a report is by totaling or subtotaling numeric values. You do this by adding fields that have the Sum or Running Sum display type applied.
Fields with the Sum display type print the total of the field’s values within a group, or within the entire report. If you add a Sum field to an additional footer for a group, it will total the items for the group. Adding Sum fields to the report footer will total all values for the entire report.
Fields with the Running Sum display type print the total of the field’s values at the point where they are placed in the entire report. They are often placed in additional footers that occur throughout a report, or in the page footer to allow running sum values to appear on each page.